It is known to improve the catalytic activity of active carbon by treatment with ammonia at high temperatures. So for instance H. P. BOHM (Fuel, 1984, Vol. 63, pages 1061-1063) has found that the treatment of active carbon with ammonia or prussic acid at temperatures above 600.degree. C. increases the catalytic activity of the active carbon in the case of oxidation reactions in the acqueous phase. However, these active carbons have the disadvantage that they are deactivated very quickly.
From U.S. Pat. No. 4 210 628 a process for the removal of nitrogen oxides from exhaust gases with the aid of ammonia is known, wherein active carbon is used as a catalyst. In the presence of sulfur oxides in the exhaust gases, on the catalyst ammonium sulfate and sulfuric acid are formed. The deactivated catalyst is therefore regenerated, e.g. by heating to temperatures between 350.degree. and 800.degree. C. in a stream of inert gas. The regenerated catalyst shows an improved catalytic activity. A pretreatment of the catalyst prior to being used in the process for the elimination of nitrogen oxides is not disclosed.